Add (non-working) test for old GCC atomic fetch_and_op builtin operations.
TEMP: fastcomp does not have __sync_fetch_and_nand, so implement it for the test.
TEMP: Route GCC atomic fetch and op builtins to library functions to make browser.test_pthread_gcc_atomic_fetch_and_op test pass.
Add test for GCC old atomic builtin __sync_op_and_fetch instructions.
TEMP: Implement __sync_op_and_fetch builtins in the test browser.test_pthread_gcc_atomic_op_and_fetch to work around that fastcomp doesn't generate these operations as atomic. TODO: Fix this in LLVM backend side.